This study plan by chess.com is a good place to start. It will guide you through a process and reveal some of the great tools on here (Tactics Trainer, Mentor, videos, etc.)
I talk about my own study plan on my blog if you are interested in another approach.
Play long time control games (at least 30 minutes) and make sure you review each game and take at least one lesson from it.
Good luck.
Please assist how can i improve my chess game